1. Field of the Invention
The present invention relates to hardening gelatin layers in photographic silver halide films.
2. Description of the Prior Art
Photographic films are commonly formed by coating two or more layers on a support. The layers comprise a wide range of aqueous dispersions of both light-sensitive and auxiliary compositions. Many films comprise two layers wherein a gelatino-silver halide emulsion is coated on the support and is then overcoated with a protective or antiabrasion layer.
A wide variety of agents are known for hardening gelatin layers in photographic silver halide films, e.g., Chrome alum, formaldehyde, glutaraldehyde, glyoxal and 1,3,5-triacrylolyl-hexahydro-S-triazone. Abele et al, U.S. Pat. No. 4,124,397, describes a process in which glutaraldehyde and its derivatives are injected into a photographic emulsion to avoid adverse effects on sensitivity and premature hardening; while Le Strange, U.S. Pat. No. 4,175,970, describes sensitization of a silver halide emulsion with a combination of glutaraldehyde and an aromatic sulfonic acid.
Glutaraldeyde is known to crosslink gelatin as much as 3600 times as fast as formaldehyde. Because of this rapid hardening action glutaraldehyde serves an important role as a hardener in developers. When it is used in a developer the sensitization and premature hardening problems associated with incorporation of glutaraldehyde in a sensitive silver halide emulsion do not occur.
It would be a significant advance to be able to employ a hardener such as glutaraldehyde directly with a silver halide emulsion and obtain rapid hardening without the drawbacks of special equipment and procedures.